Method of spreading bituminous mixtures



June 24, 1930. e. H. PERKINS 1,766,138

METHOD OF SPREADING BITUMINOUS MIXTURES Filed Dec. l8, 1928 o gmkmm :9 aa mdm (16km n24.

Patented June 24, 1930 UNITED STATES PATENT 'oFFrcr.

GEORGE HOWARD PERKINS, OF CAMBRIDGE, MASSACHUSETTS, ASSIGNOR TO WARREN BROTHERS COMPANY, OF CAMBRIDGE, MASSACHUSETTS, A CORPORATION OF WEST VIRGINIA METHOD OF SPREADING BITUMINOUS MIXTURES Application filed December 18, 1928. Serial No. 326,863.

- tion which are attained as the culmination of many years practical experience in constructing roadways of all kinds made of the materials stated, the following is believed to be a fair general statement of present practices.

Bituminous mixtures used for the wearing surfaces of sidewalks roadways or the like, or for waterproofing are ordinarily composed of mineral particles coated with bituminous cement. As the function of the bituminous cement is to bind the mineral particles together after the mixture has been spread and compacted, naturally it must be both cohesive and adhesive, hence if such a mixture is subjected to but even slight pressure it becomes coherent, due to the adhesion of the bitumen coated particles to each other.

Due to this characteristic it has not been possible, by any of the means used in the past within the knowledge of applicant, to spread such a mixture in a layer which is of uniform consistency throughout, hence when such a la er is compacted by the customary means 0 passing a heavy roller over its surface, the resultant compacted layer is not uniform in compactness throughout, but is more dense in some spotsthan in others.

In the past it has been customary to'conve such a bituminous mixture in suitable ve icles from point of preparation, to the point of use and there to'deposit and spread it in a layer of a proximately the desired depth by means 0 shovels and rakes or by some form of mechanical spreadin machine, and then to compact the layer 0 means of a roller, and in placeszinaccessible to the roller by hand tamps or equivalent means.

-When the mixture is spread by hand, that is to say, by shovels and rakes, the object of the raking is to comb the bituminous mixture so thoroughly with the tines of the rakes that the resulting layer will be not only of uniform contour, with its surface at the desired level at all points, but also to leave it in a state of uniform compactness or of uniform looscness throughout its entire depth and area. It is impossible to thus entirely overcome with the rakes, the differences in compactness, caused by the original deposition of the mixture in shovelfuls of various Volumes, striking the foundation at unequal velocities due to peculiarities inv the handling of the material by particular individuals, it being obvious that a shovelful of. coherent mixture dropped in a single-body from a height of a foot or more willlthus be compacted to a greater extent than an equal depth of the same mixture which has been cast horizontally into place, in the form of several thin layers of mixture.

All of the mechanical spreaders used for this purpose up to present date, applicant believes, are based on the princi le of deositing the mixture u on the oundation 1n piles or in long win rows in front of a screed or template held at such a-definite height above the foundation that when the screed moves forward it will ush the top of the pile of mixture forward: leaving behind the screed or template a layer of mixture of the desired depth and of uniform contour. This scraping action of the screed, however, does not in any manner correct the non-uniformity of compaction existing in various arts of the pile or piles of mixture as originally deposited in front of the screed or template. In some cases the screed is given a short reciprocating motion laterally as it progresses forward and while this assists in cutting its way'through the pile of mixture it does not correct the inequalities'of compactness-in thepile of mixture.

When a coherentv bituminous mixture has been spread by either of the above methods and is then subjected to compression by rolling, the above mentioned inequalities of compactness in various parts of the layer are corrected more or less, due to the kneading action of the roller, causing the mixture O tion, andwhen these latter spots have been compressedto the fullest degree of compaction of which they are capable, they are sufficiently stable to support the weight of the roller without further diminution of their depth, hence it is impossible for the roller to deliver any further compactionto the other spots.

, While it'is obvious that every portion of such alayerof bituminous mixture-is jof greater. vcompactness after having been 7 rolled than before, yet if the layer was non-' uniform in compactness before rolling it will still be non-uniform in compactness after rolling, though possibly the difference rtions of'the lay: er are not com acted to t e degree .of which they are capab e, they remain relatively porous and permeable to water, destroying the usefulness of such a mixture when spread for waterproofing purposes. r

If immediately after completion a street" or road with bituminous payementsurfaoe constructed in above manner is subjected to traffic in cold dry weather, such partiall compacted spots will be friable and wivabrade rapidly. If the weather is both wet i0" Y more ra idly. If the weather is hot and spots will under the kneading tion o yea and cold they will. absorb. water and abrade dry, suc action of ve icle wheels which are naturally narrower than those of the roller, be compacted to a depth less than that of adjacent spots which were fully compacted by the .roller at time of original construction and thus form depressions in'the pavement.

It. is thus obvious, that even though the bituminous surface may have been of true .even contour at the time the rolling was completed, it will soon develo irregularities of contour-due to either a rasion or to additional compaction by trafiic.

The present invention prevents the formasuch irregularities in compactness of such bituminous structures, by depositing thebituminous mixture upon the foundation, not in the form of coherent piles of variousde rees of com actness, but in the form of a s ower of in ividual, bitumen coated mineral particles or of relatively small pellets composed of a number of very small bitumen coated particles, depending upon the size of mineral particles composing the mixture.

foundation. in relative degree of compactness of adjacent portions maybe less than existed be fore rolling and as many 1 The method constituting the present in-[ ventioncomprises conveying the itunnnous mixture from convenient stock piles or eqlpivalent sources of suppl to the location w ererit' is desired to sprea same in a layer and to then comminute the mass of mixture into the. individual bitumencoated particles of which it is composed, or at least into relatively small pellets, each composed of a number of bitumen coated mineral particles, and to drop said vse arated particles or pellets, in the form 0 a shower, upon, the foundation or other surface upon which it is desired to form the layer of bituminous mixture. vThis de osition of individual particles or of smalF pellets of mixture, separately, without the application of any, ex-

ever machine is used t0\thus comminutethe ternal pressure, produces a layer which is v or portion of the t 9Q of the bitumen j mixture, it must travel overthe foundation or other surface upon which the layer is to.

be formed, so that as the individual parti-' cles or ellets emerge from the machine they will fa l in a shower directly upon the surface or foundation upon which the bituminous layer is to be formed.

I am aware that layers of mixtures may be formed by the use of socalled neumatic Y guns or nozzles, whereby '1 the bituminous p mixtur'e'is ejected by air pressure from a nozzle in the form of a spray or stream; such cases the able speed an while it is being formed, and it is not practicable by that method to form a layer which T is uniform in depth. Such pneumatic devices, however, will only handle mixturesi V which are practically non-coherent at at- .1 20 se of mosph'eric temperature, therefore such de-' vices are not applicable for the pur the present invention which is inten ed for use with bituminous pavement and sidewalk mixtures that are so adhesive and coherent that when transported in vehicles of ordinary sizethe mixture will agglomerate unarticles travel at considerstrike the surface, upon 1- which the layer :is to be formed, with con- 1.1 1 siderable force,'thus compacting'the layer:

der its own weight and when dumped'from the vehicle will not fall apart into the individual particles of which'it is composed as a load of sand would do.

I have found that the method .of spreading or depositing bituminous mixtures constituting this invention can best be carried out by use of a machine such as shown 1n the drawings attached hereto.

It is understood that this present applica-' tion is intended to cover the method described andnot to cover the machine. Application for a patent'on the machine itself is about to be filed in the Patent Office jointly by Robert C. Shoemaker of Philadelphia, Pennsylvania, and myself.

Figure 1 of the accompanying drawing 1s a side view of the machine, and

Figure 2 is a rear view.

The numbers indicate the same parts of the machine in both views. 7

The essential parts of the machine are the hopper or receptacle A in which the bituminous mixture is carried. The bottom of thehopper is'closed by the disintegrator B which consists of a chain belt which is the same width as the bottom of the hopper and which bears a series of staggered projections b on its upper side. This belt "is driven by the sprocketwheel C which in turn, is driven by a motor E through the sprocket chain e controlled bysuitable mechanism not shown. The various parts of the machine are supported on the framework F which is carried by the large wheels G which wheels may be driven in either direction, and which in turn are driven by the motor through transmission mechanism of any common construction which contains facilities for speed changes, clutch, reverse mechanism, and means for readily guiding the machine while under power.

By the means of the mechanism it is possible to cause the machine to proceed in either direction at any desired speed within a considerable range, also to operate the dis inte rator B inde endentl .of the wheels, so t at it is possib e to disintegrate and deposit the mixture in the form of a shower of separated coated particles, no matter whether the machine is stationary or moving in either direction. It is also possible to transport a hopperful of mixture without running the disintegrator.

The bituminous mixture in the hopper rests with its full weight upon the disintegratorB and when this is driven rapidly, the projections upon the upper side of the disintegrator belt, tear the mixture apart into small particles and carry particles forward and past the end of the adjustable gate I D where it is thrown off the disintegrator belt by the action of centrifugal force and is showered upon the foundation or other surface upon which the mixture is to be spread. The depth of the layer may be regu-.

lated by varying the opening of the adjustable gate D and by varyingthe speed of translation of the machine through varying the speed of revolution of the wheels The speed of the disintegratormay also be I varied but preferably is that which will develop just sufficient centrifugal forcev to throw the mixture off of the disintegrator chain as it passes the gate D. It is found ness of the same when being compressed v which comprises first comminuting said mixture in transit to provide separated bitumen coated particles and then immediately depositing said particles while still separated u on a foundation in the form of a layer of uniform density throughout.

2. The method of spreading bituminous paving mixtures to obtain uniform compactness of the same when being compressed which comprises comminuting said mixture to provide separated bitumen coated particles and then depositing the separated particles upon a foundation in the form of a shower of uniform density and advancing the shower over the foundation.

3. The method of spreading bituminous paving mixtures to obtain uniform compactness ofthe same when being compressed which comprises comminuting said mixture to provide separated bitumen coated particles, then depositing said articles upon a foundationin the form of a shower and varying the rate of deposit of the shower.

Tn testimon GEOR whereof I afiix my si nature. 

